I think etiquette dictates that if you receive a gift in person and have the opportunity to thank the giver then, a thank you note is unnecessary. But I like sending thank you notes and am a stickler about them. I don't expect them from people I give gifts to, because they seem to be falling out of custom, but I always appreciate them. And older generations often do expect them, so not sending one could indeed be offensive to them.

And I will admit that I've stopped gifting one friend because she could never be bothered to reciprocate my gift-giving or even acknowledge it with a phone call or card. After about eight years of unmentioned wedding, birthday, Christmas, and baby gifts I've just stopped giving her anything.

That said, complaining about someone else's poor etiquette is incredibly rude. If your aunt indeed did so (this is all hearsay through your grandmother though, so be careful here), she was much ruder than you were IMHO. (But I agree that you should send thank you notes for your wedding gifts.)

Dear Aunt, Thank you for the "Even though you're a Jew, Jesus still loves you" plaque. It was so kind of you to think of us! We loved seeing you at our wedding, you can really cut a rug! Love, Niece and Nephew-in-law